While the invention is by no means limited to being used in conjunction with a conventional thermal power plant, for simplicity, in the following description the invention will be described in conjunction with an otherwise conventional thermal power plant using water as the working fluid and operating a steam cycle.
A conventional thermal power plant is operated using demineralised water as the working fluid that is heated to a vapour in a boiler and expanded through a number of turbines in series, or in parallel, or in a combination of series and parallel, to drive generators to generate electricity. The expanded vapour is then condensed in a cooling system to a liquid and returned to the boiler where the water is reheated to steam to repeat the power generation cycle.
The cooling system is typically a wet system and includes a condenser, one or more cooling towers and a recirculation pump.
In a wet cooling system, the expanded steam is condensed in the condenser by heat exchange with cooling feed water typically extracted from a naturally occurring body of water such as the sea, a river, a lake or a reservoir. The feed water is typically circulated through pipes in the condenser around which the expanded steam flows and condenses on the cold surface of the pipes. However, in an alternative arrangement, the cold feed water is sprayed onto pipes through which the expanded steam is circulated, thereby condensing the steam.
The feed water heated up in the condenser by the expanded steam is pumped to the cooling towers and sprayed onto rocks inside the towers. The feed water is cooled by heat exchange with colder, outside, air that enters at the base of the cooling tower and rises up the cooling tower as it is heated by the hotter feed water. This creates a natural updraft of air inside the cooling tower which is assisted by any prevailing wind passing over the top of the cooling tower, creating a draw. The feed water is collected in a reservoir at the base of the cooling tower and is recirculated by the pump through the condenser, or released to the naturally occurring body of water and replaced by a fresh supply of cooling feed water.
Problems with wet cooling include the requirement for a ready source of cooling feed water, the large expanse of land required to accommodate the several large cooling towers that are often required for a single power plant, and the need to comply with legislation that typically stipulates that the waste feed water must be cooled to a certain temperature before being returned to the source in order to prevent a rise in the temperature of the source affecting local eco-systems. These problems mean that it is more difficult to locate power plants and their associated cooling towers in built-up areas. The operation of cooling the feed water also uses energy from the power plant leading to a reduction in net useable energy from the power station and an associated reduction in system efficiency.
An alternative thermal power plant, such as the Matimba Power Plant in Ellisras, South Africa, employs an air-cooled condenser in which ambient air is used to cool steam expanded in a steam turbine. The expanded steam is circulated through pipes in the condenser around which cold air flows to cool and condense the steam before it is returned to the boiler. Sometimes, for example at Scottish Power's Rye House power station, large electric fans (blade diameters typically of the order of 6 meters) blow air over the cooling pipes to enhance cooling.
A problem of air cooled condensers is that they are typically larger and more expensive to build and operate, and are less efficient at condensing an expanded vapour, than conventional water-cooled condensers such as that described above.